The Hubble website contains lots of amazing photos of the universe. I have scaled down some of them so that they can be used as desktop backgrounds.
All files have been carefully cropped from raw files with the highest resolution I could find. They are saved in the lossless PNG format, which take up more space than files in the JPG format but have somewhat better quality. As a desktop background file is read in once at startup time, the file size isn't an issue anyway.
Each desktop background image is available in several common screen dimensions. If the screen size you need is not included, leave a comment.
Click on the links below to see more details about the objects and to access the desktop backgrounds.